1. Field of the Invention
The present invention relates to a wavelength converter, and more particularly, to a wavelength converter which can easily be matched with an optical fiber bundle.
2. Description of the Related Art
Semiconductor optical amplifiers (SOAs) use the gain characteristic of a semiconductor to amplify a light signal. When input light passes an SOA, output light is amplified by the gain of the SOA. SOAs are fundamentally very similar to semiconductor laser devices.
For a wavelength conversion device, an SOA and a passive wave guide are formed on a single substrate, and a wavelength is converted due to a change in the refractivity of a medium, which is caused by interference between input light and pumping light, and due to a cross phase modulation (XPM) effect, which is caused by the change in the refractivity.
The combination of an SOA and a passive waveguide is implemented by monolithic integration or hybrid integration. Hybrid integration, which employs a planar lightwave circuit (PLC) as a waveguide, has been highlighted because it is simple to manufacture and it has a low coupling loss.
In such a conventional wavelength converter, optical fibers are provided at both ends of a substrate, and thus optical fibers must be coupled to ports one to one. However, in such a structure in which the ports are separated at both sides of the substrate, it is very difficult to arrange fibers, and thus the yield of a wavelength converter module is very low and the cost is very high. What is needed is a wavelength converter where the input and the output ends are on the same side of the substrate of the wavelength converter, thus allowing only one optical fiber bundle to be connected to the wavelength converter.
To solve the above problem, it is an object of the present invention is to provide a wavelength converter for facilitating the convenient arrangement of optical fibers.
It is yet another object of the present invention is to provide a wavelength converter for reducing the manufacturing cost and increasing yield.
It is further an object to provide a wavelength converter where the input and the output of the wavelength converter are on the same side of the wavelength converter and in close proximity with each other.
It is still another object of the present invention to provide a wavelength converter that allows only one optical fiber bundle to be connected to the wavelength converter, the optical bundle containing fibers for both the inputs and the output of the wavelength converter.
To achieve the above objects of the invention, there is provided a wavelength converter including a substrate; first and second semiconductor optical amplifiers (SOAs) provided in parallel on the substrate, each of the SOAs including a first portion which passes light at one end, and a second portion which passes light at the opposite end; a first waveguide connected to the second portions of the first and second SOAs; a second waveguide connected to the first portion of the first SOA; and a third waveguide connected to the first portions of the first and second SOAs. The first through third waveguides are arranged on one side of the substrate in the vicinity of the first portions of the first and second SOAs. The first waveguide is connected to the second portions of the first and second SOAs through a unit for changing an optical progressing path.
Preferably, the wavelength converter further includes an antireflective coating layer on one end facet of the substrate on which the waveguides are arranged.
The first waveguide includes a first path extending from the second portions of the first and second SOAs toward one end of the substrate facing the second portions, a second path extending in a direction perpendicular to the first path, and a third path extending from the second path back toward the side of the substrate where the first through third waveguides are arranged, the third path disposed in parallel to the second and third waveguides. Particularly, the unit for changing an optical progressing path includes first and second mirrors, which are provided at the intersection of the first and second paths of the first waveguide and at the intersection of the second and third paths of the first waveguide, respectively. It is preferable that each of the first and second mirrors is realized as one facet of an etched portion formed on the substrate.
In another embodiment, the first waveguide includes a first path expending from the second portions of the first and second SOAs toward one end of the substrate facing the second portions, an arc-shaped second path extending from the first path and curving toward the side of the substrate where the first through third waveguides are arranged in an arc shape, the second path providing the unit for changing an optical progressing path, and a third path extending from the second path back toward the side of the substrate where the first through third waveguides are arranged, the third path disposed in parallel to the second and third waveguides.